reaching a height of from twenty to twenty-five feet. In some the ears are only an inch or two long; in others as much as sixteen inches. The number of kernel rows, which is always even, ranges from eight to twenty-four or more, according to variety. Abnormal individual ears sometimes have as few as four in some varieties, or as many as forty-eight in the large-eared sorts. The size of the kernels, their shape, colour, chemical composition, etc., are extremely variable. According to Dr. E. L. Sturtevant, the varieties may be classified into the following seven principal groups.
i. The pod corns have each kernel enclosed in a pod or small husk and the ear thus formed is also enclosed in husks. All other groups have naked kernels within the husks. It is doubtful, however, whether the pod corns form a natural group. Possibly the husks surrounding the kernels are abnormal and might be found in any of the main groups. This opinion is supported by the fact that the kernel structure varies in the pod corns.
The pop corns are characterized by an excessive proportion of the corneous endosperm; that is, the nutritious matter, which forms the greater part of the kernel and is stored for the use of the sprouting germ, contains little starch. In this group the kernels and ears are small. The property of popping over a fire, which is the complete turning inside out of the kernel through the explosion of its moisture content, is most pronounced in varieties which have a corneous endosperm throughout and is less marked as the percentage of starch increases.
The flint corns may be recognized by the central part of the endosperm being starchy and completely surrounded by a corneous coat, varying in thickness in different varieties. Cartier found varieties of this group in the neighbourhood of Montreal.
The dent corns have the central starchy part of the endosperm surrounded by a corneous layer at the sides of the kernel only, the starchy endosperm thus extending to the summit of the kernel. When the endosperm dries and shrinks, various indentations are formed on the summit of the kernel. The dent corns are extensively grown in the United States, the number of varieties exceeding that of all other varieties combined.
The soft corns have no corneous endosperm. The shrinkage in ripening is therefore uniform in all parts of the kernel. To this group belong the mummy corns of Peru and Chili.